Low-maintenance coating technology

ABSTRACT

The invention provides a substrate bearing a low-maintenance coating. In some embodiments, the coating includes a low-maintenance film that includes a thickness of film comprising titania, wherein only part of that thickness includes tungsten. The thickness includes an inner portion and an outer portion, the outer portion being the part that includes tungsten. The invention also provides methods and equipment for depositing such coatings.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Application No.60/972,527, filed Sep. 14, 2007, and U.S. Application No. 61/039,760,filed Mar. 26, 2008, the entire disclosures of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention provides thin film coatings for substrates. Moreparticularly, the invention provides low-maintenance coatings for glassand other substrates. The invention also provides methods for producinglow-maintenance products. Further, the invention provides sputteringtargets and coaters.

BACKGROUND OF THE INVENTION

Low-maintenance coatings, for example photocatalytic coatings, are wellknown in the present art. A great deal of research has been done inattempting to develop low-maintenance coatings that exhibit goodproperties, such as self-cleaning properties and hydrophilicity.

Most conventional low-maintenance coatings include a layer of titaniumdioxide (i.e., TiO₂). While many of these coatings are advantageous,there is room for improvement. For example, it would be desirable toprovide thin low-maintenance coatings that have low visible reflectionand good color neutrality, and yet can achieve significant photoactivitylevels, hydrophilicity, and/or activation ability. It would beparticularly desirable to provide coatings that achieve these propertieswhile at the same time are durable, stable, and resistant to hazeformation (e.g., during tempering or other heat treatments).

SUMMARY OF THE INVENTION

A substrate having a major surface on which there is a low-maintenancecoating is provided, in accordance with certain embodiments. Thelow-maintenance coating provides photocatalytic and/or hydrophilicproperties and is preferably has properties that are easily activated.The low-maintenance coating can include a thickness of film comprisingtitania, said thickness being less than 250 Å, wherein only part of thatthickness includes tungsten oxide, said thickness including an innerportion and an outer portion, the inner portion being closer to thesubstrate than is the outer portion, the outer portion being the partthat includes tungsten oxide. The low-maintenance coating can have athickness of less than 300 Å. The thickness of the film comprisingtitania can be greater than about 50 Å. Likewise, the thickness of theouter portion can be no more than about 90 Å. The outer portion can alsodefine an exposed, outermost face of the low-maintenance coating, theouter portion being a substantially homogenous film comprising bothtitanium dioxide and tungsten oxide. The outer portion can furthercomprise nitrogen. The inner portion can be a substantially homogenousfilm consisting essentially of titania. In some cases, the outer portioncan have a tungsten load characterized by a metal-only atomic ratio ofbetween about 0.01 and about 0.34, this ratio being the number oftungsten atoms in the outer portion divided by the number of titaniumatoms in the outer portion.

The low maintenance coating can also include a base film, which cancomprise silica or alumina in some embodiments. The base film can alsohave a thickness of less than about 100 Å. The low maintenance coatingcan also include an intermediate film provided on the base film, whichcan have a thickness of less than 100 Å in some embodiments. In certaincases, the base film comprises alumina and the intermediate filmcomprises silica, and the alumina base film and the intermediate silicafilm each have a thickness of less than about 50 Å. In one embodiment,the alumina base film has a thickness of about 40 Å, and the silicaintermediate film has a thickness of about 30 Å. The low-maintenancecoating can optionally be over a transparent conductive oxide film,which can have a thickness of less than about 10,000 Å. The substratemay, for example, be a transparent pane that is part of a multiple-paneinsulating glazing unit having a between-pane space, wherein the majorsurface bearing the low-maintenance coating faces away from thebetween-pane space of the unit.

A method of producing a low-maintenance product is provided, inaccordance with certain embodiments. The method can include depositing alow-maintenance coating on a major surface of a substrate, thelow-maintenance coating including a thickness of film comprisingtitania, wherein only part of that thickness includes tungsten oxide,wherein the thickness of film comprising titania includes an innerportion and an outer portion, the outer portion being the part thatincludes tungsten oxide, the inner portion being deposited before theouter portion is deposited, and wherein the substrate is subjected toheating after the inner portion has been deposited but before the outerportion is deposited. The substrate can also be subjected to heatingbefore the inner portion has been deposited or even during deposition ofeither the inner portion and outer portion. In addition, thelow-maintenance coating can be deposited in a sputter coater, whereinsaid heating is performed inside the coater, and wherein said heatingbrings the substrate to a maximum temperature of greater than 140° F.but less than 350° F. In some cases, the heating is performed inside ofa deposition chamber that is adapted for depositing the inner portion,the heating taking place after the inner portion is deposited. In othercases, the heating is performed inside of a deposition chamber that isadapted for depositing the outer portion, the heating taking placebefore the outer portion is deposited. In yet other cases, the heatingis performed inside of a heating chamber that is adapted for depositingthe inner portion and a second deposition chamber that is adapted fordepositing the outer portion. The method can also include conveying thesubstrate through one or more inter-stage sections that are part of acoater, the inter-stage sections being adapted for maintaining thesubstrate at a temperature of at least 160° F. In some cases, at leastone of the inter-stage sections is positioned between a first depositionchamber adapted for depositing the inner portion and a second depositionchamber that is adapted for depositing the outer section.

Another method of producing a low-maintenance product is provided, inaccordance with other embodiments. The method can include providing asubstrate having a major surface on which there is a low-maintenancecoating, the low-maintenance coating including a thickness of filmcomprising titania, said thickness being greater than about 50 Å butless than 250 Å, wherein only part of that thickness includes tungstenoxide, said thickness including an inner portion and an outer portion,the inner portion being closer to the substrate than is the outerportion, the outer portion being the part that includes tungsten oxide,the method further comprising heat treating said coated substrate tobring it to a temperature of at least about 160° F. In some cases, theheat treating is accomplished by positioning the coated substrate in aheating chamber for at least 60 seconds during which time the heatingchamber is maintained at a temperature of at least 650° C. In othercases, the heat treating is accomplished by heat treating the coatedsubstrate inside of a deposition chamber that is adapted for depositingeither the inner portion or the outer portion. The heat treating caninclude heating during deposition and/or before deposition and/or afterdeposition. The method can further include cooling the coated substrateback down to room temperature, at which point the coated substrateexhibits a haze of less than about 0.4. This cooling can be performed onsubstrates wherein the thickness of the outer portion is no more thanabout 90 Å.

A sputtering technique for depositing a low-maintenance coating over amajor surface of a substrate is also provided, in accordance withcertain embodiments. The sputtering technique can include depositing athickness of film comprising titania, wherein at least part of thatthickness includes tungsten oxide and is deposited by sputtering one ormore targets having a sputterable material comprising both titania andtungsten oxide, wherein the sputterable material includes: i) tungstenin oxide form, ii) TiO, and iii) TiO₂. In some cases, substantially allthe tungsten in the sputterable material is in oxide form. Thedepositing can also be accomplished by sputtering the targets in anatmosphere comprising argon and oxygen. The depositing can also beaccomplished by sputtering the targets in an atmosphere comprisingargon, oxygen, and nitrogen. In some cases, the sputterable material ischaracterized by a metal-only atomic ratio of between about 0.01 andabout 0.34, this ratio being the number of tungsten atoms in thesputterable material divided by the number of titanium atoms in thesputterable material. The thickness of film comprising titania beingdeposited can include an inner portion and an outer portion, the innerportion being closer to the substrate than is the outer portion, whereinonly the outer portion includes tungsten oxide, the outer portion beingdeposited as a substantially homogenous film comprising titanium oxideand tungsten oxide. The inner portion can also be deposited as filmconsisting essentially of titania. The thickness of the film comprisingtitania can also be less than 250 Å.

A sputtering target is also provided, in accordance with certainembodiments. The target can have a sputterable material comprising bothtitania and tungsten oxide, wherein the sputterable material includes:i) tungsten in oxide form, ii) TiO, and iii) TiO₂. In some cases,substantially all the tungsten in the sputterable material is in oxideform. In certain cases, the sputterable material consists essentiallyof: i) tungsten in oxide form, ii) TiO, and iii) TiO₂. The sputterablematerial can also have a metal-only atomic ratio between about 0.01 andabout 0.34, this ratio being the number of tungsten atoms in thesputterable material divided by the number of titanium atoms in thesputterable material. The target can be a cylindrical rotary target, thesputterable material being carried on an exterior wall of an elongatedbacking tube, the elongated backing tube having a length of at least 24inches, the target being adapted to rotate about a central axis to whichthe exterior wall of the backing tube is substantially parallel.

A sputter coater is also provided, in accordance with certainembodiments. The sputter coater can include two or more chambers thatinclude sputtering chambers and/or heating chambers. The coater can alsoinclude at least one inter-stage section connecting the two or morechambers. For example, the inter-stage section can connect twosputtering chambers or a heating chamber and a sputtering chamber. Theinter-stage section can also have an interior space that is surroundedby alternating layers of a conductive metal and a ceramic material. Atleast one heating source can be provided that applies heat to theinter-stage section, so that the interior space is maintained at atemperature of at least 160° F. In some cases, the coater is adapted fordepositing a thickness of film comprising titania, wherein only a partof that thickness includes tungsten oxide, the thickness including aninner portion and an outer portion, the inner portion being closer tothe substrate than the outer portion, the outer portion being the partthat includes tungsten oxide. In these cases, the inter-stage sectioncan connect a first sputtering chamber that is adapted for depositingthe inner portion and a second sputtering chamber that is adapted fordepositing the outer portion. The inter-stage section can also connect aheating chamber and a sputtering chamber that is adapted for depositingthe outer portion.

In certain embodiments, the invention provides a substrate having amajor surface on which the following films are coated in sequence,moving outwardly from the major surface: (1) a functional filmcomprising a material selected from the group consisting of indium tinoxide and fluorine-containing tin oxide; and (2) a thickness of filmcomprising titania. Only part of that thickness includes tungsten oxide.The thickness of film comprising titania includes an inner portion andan outer portion. The inner portion is closer to the substrate than isthe outer portion. And the outer portion is the part that includestungsten oxide. In the present embodiments, a thickness ratio defined asthe thickness of film comprising titania divided by the thickness of thefunctional film can optionally be between about 0.004 and about 0.08.

Some embodiments provide a substrate having a major surface on whichthere is both a transparent conductive oxide film and a low-maintenancecoating. The transparent conductive oxide film is closer to thesubstrate than is the low-maintenance coating. The low-maintenancecoating includes a thickness of film comprising titania, and only partof that thickness includes tungsten oxide. The thickness of filmcomprising titania includes an inner portion and an outer portion. Theinner portion is closer to the substrate than is the outer portion. Theouter portion is the part that includes tungsten oxide. Between thetransparent conductive oxide film and the thickness of film comprisingtitania, there can optionally be two layers including one comprisingsilica and one comprising alumina.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a substrate having a majorsurface carrying a low-maintenance coating in accordance with certainembodiments;

FIG. 2 is a schematic cross-sectional view of a substrate having a majorsurface carrying a low-maintenance coating in accordance with certainembodiments;

FIG. 3 is a schematic cross-sectional view of a substrate having a majorsurface carrying a low-maintenance coating in accordance with certainembodiments;

FIG. 4 is a schematic cross-sectional view of a substrate having a majorsurface carrying a low-maintenance coating in accordance with certainembodiments;

FIG. 5 is a schematic cross-sectional view of a substrate having a majorsurface carrying a low-maintenance coating in accordance with certainembodiments;

FIG. 6 is a schematic cross-sectional view of a substrate having onesurface carrying a low-maintenance coating and another surface carryingan additional functional coating in accordance with another embodiment;

FIG. 7 is a partially broken-away schematic cross-sectional side view ofa multiple-pane insulating glazing unit that includes an exterior panehaving a first surface carrying a low-maintenance coating and a secondsurface carrying an additional functional coating in accordance withcertain embodiments;

FIG. 8 is a partially broken-away schematic cross-sectional side view ofa multiple-pane insulating glazing unit that includes an exterior panehaving a second surface carrying a functional coating and an interiorpane having a fourth surface carrying a low-maintenance coating inaccordance with certain embodiments;

FIG. 9 is a partially broken-away perspective view of a window panehaving a major surface carrying a low-maintenance coating, the panebeing mounted in an exterior wall of a building in accordance withcertain embodiments;

FIG. 10 is a schematic side view of a downward sputtering chamberadapted for use in certain methods;

FIG. 11 is a schematic side view of an upward sputtering chamber adaptedfor use in certain methods;

FIG. 12 is a schematic side view of a dual-direction sputtering chamberadapted for use in certain methods;

FIG. 13 is a schematic side view of a downward heating chamber adaptedfor use in certain methods;

FIG. 14 is a schematic side view of an upward heating chamber adaptedfor use in certain methods;

FIG. 15 is a schematic side view of an inter-stage section adapted foruse in certain methods;

FIG. 16 is a front cross-section view of an inter-stage section adaptedfor use in certain methods;

FIG. 17 is a schematic side view of a coating line, including downwardsputtering chambers and a downward heating chamber, which is adapted foruse in certain methods;

FIG. 18 is a schematic side view of a coating line, including upwardsputtering chambers and an upward heating chamber, which is adapted foruse in certain methods;

FIG. 19 is a schematic side view of a coating line, including upwardsputtering chambers and an upward heating chamber, which is adapted foruse in certain methods;

FIG. 20 is a schematic side view of a coating line, including upwardsputtering chambers and an upward heating chamber, which is adapted foruse in certain methods; and

FIG. 21 is a chart illustrating the rate of acetone photodecompositionfor two coatings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is to be read with reference to thedrawings, in which like elements in different drawings have likereference numbers. The drawings, which are not necessarily to scale,depict selected embodiments and are not intended to limit the scope ofthe invention. Skilled artisans will recognize that the given exampleshave many alternatives that fall within the scope of the invention.

Many embodiments of the invention involve a coated substrate. A widevariety of substrate types are suitable for use in the invention. Insome embodiments, the substrate 10 is a sheet-like substrate havinggenerally opposed first 12 and second 14 major surfaces. For example,the substrate can be a sheet of transparent material (i.e., atransparent sheet). The substrate, however, is not required to be asheet, nor is it required to be transparent.

The substrate can optionally be a component of any of a variety ofbuilding materials. Examples of anticipated applications includeembodiments wherein the substrate is a sash (e.g., a window sash or adoor sash), a siding panel (e.g., an aluminum siding panel), a tentpanel, a tarpaulin (e.g., a fluorocarbon polymer tarpaulin), a plasticfilm (e.g., a fluorocarbon plastic film), a roofing shingle, a windowblind (such as a metal, plastic, or paper window blind), a paper screen(e.g., a shoji), a railing, a baluster, or an escutcheon. In oneembodiment, the substrate is a ceramic tile, such as a wall, ceiling, orfloor tile. In another embodiment, the substrate is a glass block. Avariety of suitable glass blocks can be obtained commercially fromSaint-Gobain Oberland (Koblenz, Germany). In still other embodiments,the substrate is a polyester film, a polyethylene film, a terephthalatefilm, etc. Suitable films of this nature can be obtained commerciallyfrom Nippon Soda Co., Ltd. (Tokyo, Japan). In further embodiments, thesubstrate is a fence or wall, such as a noise-reduction fence or wall.The substrate can alternatively be part of a photovoltaic device (e.g.,it can be a cover for a photovoltaic device).

For many applications, the substrate will comprise a transparent (or atleast translucent) material, such as glass or clear plastic. Forexample, the substrate is a glass sheet (e.g., a window pane) in certainembodiments. A variety of known glass types can be used, and soda-limeglass will commonly be preferred. In certain preferred embodiments, thesubstrate is part of a window, skylight, door, shower door, or otherglazing. In some cases, the substrate is part of an automobilewindshield, an automobile side window, an exterior or interior rear-viewmirror, a bumper, a hubcap, a windshield wiper, or an automobile hoodpanel, side panel, trunk panel, or roof panel. In other embodiments, thesubstrate is a piece of aquarium glass, a plastic aquarium window, or apiece of greenhouse glass. In a further embodiment, the substrate is arefrigerator panel, such as part of a refrigerator door or window. Inanother embodiment, the substrate is part of an electrochromic device.

Substrates of various sizes can be used in the present invention.Commonly, large-area substrates are used. Certain embodiments involve asubstrate 10 having a major dimension (e.g., a length or width) of atleast about 0.5 meter, preferably at least about 1 meter, perhaps morepreferably at least about 1.5 meters (e.g., between about 2 meters andabout 4 meters), and in some cases at least about 3 meters. In someembodiments, the substrate is a jumbo glass sheet having a length and/orwidth that is between about 3 meters and about 10 meters, e.g., a glasssheet having a width of about 3.5 meters and a length of about 6.5meters. Substrates having a length and/or width of greater than about 10meters are also anticipated.

In some embodiments, the substrate 10 is a generally square orrectangular glass sheet. The substrate in these embodiments can have anyof the dimensions described in the preceding paragraph and/or in thefollowing paragraph. In one particular embodiment, the substrate is agenerally rectangular glass sheet having a width of between about 3meters and about 5 meters, such as about 3.5 meters, and a length ofbetween about 6 meters and about 10 meters, such as about 6.5 meters.

Substrates of various thicknesses can be used in the present invention.In some embodiments, the substrate 10 (which can optionally be a glasssheet) has a thickness of about 1-5 mm. Certain embodiments involve asubstrate 10 with a thickness of between about 2.3 mm and about 4.8 mm,and perhaps more preferably between about 2.5 mm and about 4.8 mm. Inone particular embodiment, a sheet of glass (e.g., soda-lime glass) witha thickness of about 3 mm is used. In one group of embodiments, thethickness of the substrate is between about 4 mm and about 20 mm.Thicknesses in this range, for example, may be useful for aquarium tanks(in which case, the substrate can optionally be glass or acrylic). Whenthe substrate is float glass, it will commonly have a thickness ofbetween about 4 mm and about 19 mm. In another group of embodiments, thesubstrate is a thin sheet having a thickness of between about 0.35 mmand about 1.9 mm. Embodiments of this nature can optionally involve thesubstrate 10 being a sheet of display glass or the like.

With reference to FIG. 1, there is shown a substrate 10 with a majorsurface 12 bearing a low-maintenance coating 80. The low-maintenancecoating 80 preferably has photocatalytic properties, hydrophilicproperties, or both. The low-maintenance coating 80 includes a thicknessof film comprising titania 50. The film 50 includes an inner portion 50a and an outer portion 50 b. The inner portion 50 a is closer to thesubstrate than is the outer portion 50 b. In come cases, there may be adiscrete interface between the inner 50 a and outer 50 b portions of thefilm comprising titania, as shown in FIG. 3. For example, the inner 50 aand outer 50 b portions may be separate layers having a relativelywell-defined interface. This may be the case, for example, when two suchlayers are initially deposited by sputtering. Alternatively, these twoportions 50 a, 50 b may be graded into each other, or their interfacemay be otherwise blurred.

In some embodiments, the outer portion 50 b defines an exposed,outermost face of the low-maintenance coating. The outer portion 50 bcomprises both titanium (e.g., titania) and tungsten (e.g., tungstenoxide). In some cases, the outer portion comprises titania and tungstenoxide. In certain cases, substantially all (or all) of the tungsten inthe outer portion 50 b is in oxide form. Preferably, the outer portion50 b contains more titania than tungsten oxide. In some embodiments, theouter portion 50 b has between about 1-6 atomic percent tungsten, suchas about 2.0-2.5 atomic percent (on a metal only basis). The outerportion 50 b can optionally be a substantially homogenous filmcomprising both titania (e.g., TiO₂) and tungsten oxide. If desired, theouter portion 50 b can consist essentially of titania and tungstenoxide. This, however, is not strictly required.

The inventors have found that adding tungsten oxide to a film comprisingtitania can increase photoactivity and hydrophilicity. However, a thickfilm of titania and tungsten oxide may be limited in terms of hazeresistance, durability, and stability. Surprisingly, the inventors havediscovered that incorporating tungsten oxide into a limited outerportion of a titania film can provide good photoactivity andhydrophilicity while at the same time achieving good haze resistance,durability, and stability.

The film comprising titania 50 can include TiO₂, TiO, or both. Otherforms of titanium oxide, such as TiO_(x), may also be present. Incertain embodiments, the film 50 includes titania and an additionalmaterial, e.g., a material selected from the group consisting ofnitrogen, tantalum, copper, silica, palladium, tin, niobium, andmolybdenum. Other “additional materials” can also be used. Theadditional material may, for example, be a dopant that is present in anamount of up to five atomic percent, e.g., about two atomic percent orless. Larger concentrations may be preferred in other cases. Theadditional material, when provided, can be present throughout the innerportion 50 a, the outer portion 50 b, or both. It may be preferred,though, for the outer portion 50 b to consist essentially of titania andtungsten oxide. It may also be preferred for the inner portion 50 a toconsist essentially of titania.

In some cases, the film 50 includes nitrogen. When provided, thenitrogen preferably is present in an amount of up to 10 percent or less,and more preferably 5% or less. When provided, the nitrogen may bepresent only in the inner portion 50 a, only in the outer portion 50 b,or in both the inner portion 50 a and outer portion 50 b.

The inner portion 50 a can be a substantially homogenous film, a gradedfilm, or some other type of non-homogenous film. In certain embodiments,the inner portion 50 a is a substantially homogenous film comprising(optionally consisting essentially of) titania. In other embodiments,the inner portion 50 a is a substantially homogenous film comprising(optionally consisting essentially of) titania and an additionalmaterial (such as one of the additional materials noted above).

The outer portion 50 b can also be a substantially homogenous film, agraded film, or some other type of non-homogenous film. In certainembodiments, the outer portion 50 b is a substantially homogenous filmcomprising (optionally consisting essentially of) titania and tungstenoxide. In other embodiments, the outer portion 50 b is a substantiallyhomogenous film comprising (optionally consisting essentially of)titania, tungsten oxide, and an additional material (such as one ofthose noted above).

In one group of embodiments, both the inner portion 50 a and the outerportion 50 b are substantially homogenous films. For example, the innerportion 50 a can be a substantially homogenous film consistingessentially of titania, and the outer portion 50 b can be asubstantially homogenous film consisting essentially of titania andtungsten oxide. This, however, is by no means required.

In certain embodiments, the inner portion 50 a has a thickness ofbetween about 15 Å and about 100 Å, such as between about 15 Å and about30 Å. In certain cases, the inner portion 50 a has a thickness of about25 Å. In other embodiments, though, the thickness of the inner portion50 a can be varied considerably outside these ranges to accommodate therequirements of different applications.

In connection with the outer portion 50 b, the inventors have discoveredthat when the thickness of this portion is less than about 100 Å,preferably less than about 90 Å, and perhaps optimally less than about75 Å(or even less than about 50 Å), the coating 80 can achieve anexceptional degree of haze resistance. For example, the haze of a glasspane carrying the present low-maintenance coating 80 can be less than0.40 after tempering, or even less than 0.30, such as between about 0.2and about 0.27. In preferred embodiments, the outer portion 50 b has athickness of between about 15 Å and about 100 Å, such as between about20 Å and about 90 Å, e.g., between about 30 Å and about 75 Å. In certainembodiments, the outer portion 50 b has a thickness of about 45 Å. Hereagain, the thickness can be chosen to be well outside these ranges tomeet the requirements of different applications.

The total thickness of the film comprising titania 50 (including boththe inner portion 50 a and the outer portion 50 b) preferably is lessthan 250 Å, more preferably less than 200 Å, perhaps less than 150 Å, oreven less than 100 Å. The inventors have found that these thicknessranges are particularly advantageous in minimizing, or even eliminating,the color that can occur with thicker films of this particular nature.In other embodiments, though, thicker films may be used for applicationswhere more color is desirable, or at least acceptable, or where anothercoating or pane neutralizes the color adequately.

The inventors have also discovered that if the thickness of the filmcomprising titania 50 is greater than about 50 Å, then there is asurprising boost in photoactivity, hydrophilicity, or both when thecoated substrate is tempered or otherwise heat treated appropriately.When this thickness is less than about 50 Å, however, tempering does notappear to provide such a boost. Thicknesses of about 70 Å or greater arepreferred in this regard. The mechanism behind this surprising boost inproperties has not been definitively explained. It is surmised, however,that when the coated substrate is heat-treated, this causes a decreasein density of defect states of the film allowing the photoexcitedelectrons in the conduction band of the titania to have a longerlifetime resulting in an increase in quantum efficiency. The improvedquantum efficiency results in more electron-hole pairs to generatehydroxyl radicals (OH.) and superoxide ions (O₂ ⁻) to decompose andmineralize organic compounds by participating in a series of oxidationreactions. This results in a favorable change in photoactivity,hydrophilicity, or both. The inventors, though, do not wish to be boundby this explanation.

In one group of embodiments, the low-maintenance coating 80 has a“region ratio” of between 0.2 and 7. The term “region ratio” is definedas the thickness of the outer portion 50 b divided by the thickness ofthe inner portion 50 a. In some cases, the outer portion 50 b is thinnerthan the inner portion 50 a. This may be preferred when haze resistanceis a primary concern. In other cases, though, the outer portion 50 b isthicker than the inner portion 50 a. This may be preferred formaximizing the photoactivity and hydrophilicity. Table 1 below depictsone exemplary embodiment of this nature.

In certain embodiments, the outer portion 50 b has a tungsten loadcharacterized by a metal-only atomic ratio of between about 0.001 and0.4, such as between about 0.01 and about 0.34. This ratio is the numberof tungsten atoms in the outer part 50 b divided by the number oftitanium atoms in the outer part. In one example, the outer portion 50 bis deposited by reactively sputtering one or more ceramic targets eachhaving about 91 atomic % titanium and about 9 atomic % tungsten (on ametal-only basis). In the resulting oxide film, the relative amount oftungsten may be slightly higher than in the target. For example, theoxide film may have about 89 atomic % titanium and about 11 atomic %tungsten (again, on a metal-only basis), in which case the specifiedmetal-only atomic ratio is about 0.12. In another example, the resultingouter portion 50 b is an oxide film having 97.5 atomic % titanium andabout 2.5 atomic % tungsten, in which case the specified metal-onlyatomic ratio is about 0.26%. It is to be appreciated that the outerportion 50 b may be an oxide film, an oxynitride film, etc.

With reference to FIG. 2, in some embodiments, the low-maintenancecoating 80 includes a base film 15 between the film 50 comprisingtitania and the substrate 10. The base film 15 can be any suitablematerial that adheres well to the substrate and/or protects the film 50from sodium ion diffusion. In cases where the base film 15 is omitted,the substrate 10 itself can be treated to reduce or perhaps deplete thesurface area of the substrate of sodium ions. The base film 15 cancomprise a dielectric film in some embodiments. In certain embodiments,the base film comprises silica, alumina, or both. Thus, the base film 15can optionally be a mixed film including two or more materials. In somecases, it is a mixed film comprising silica and alumina, or silica andtitania, or silica, alumina and titania. Other materials can be used aswell. In certain embodiments, the base film consists essentially ofsilica, or consists essentially of alumina. The base film 15 can also bea substantially homogenous film or a graded film. When provided, thebase film 15 may be deposited directly onto the substrate, with the filmcomprising titania 50 being deposited directly onto the base film 15.This, however, is by no means required. When provided, the base film 15can optionally have a thickness of less than about 300 Å. In certainembodiments, the base film 15 has a thickness of less than 120 Å or evenless than 100 Å. In some embodiments, the base film 15 has a thicknessof less than 50 Å, such as about 30 Å.

In certain embodiments, the base film 15 comprises both silica andalumina. For example the film can have a thickness (e.g., of about 70Å), wherein the entire thickness comprises a mixed film (or a gradedfilm) comprising silica and alumina. The mixed film can be formed bysputtering an alloy target that includes silicon and aluminum, forexample about 50% silicon and about 50% aluminum, or about 25% siliconand about 75% aluminum, about 75% silicon and about 25% aluminum, orabout 85% silicon and about 15% aluminum. Such an alloy target can besputtered in an oxidizing atmosphere. The mixed film can also be formedby co-sputtering two targets, wherein one target is a silicon target andthe other target is an aluminum target. Such co-sputtering can beperformed in an oxidizing atmosphere. In other embodiments, the basefilm 15 includes an inner layer and an outer layer, wherein the innerlayer comprises one of silica or alumina and the outer layer comprisesthe other of silica or alumina. In some cases, the inner layer has athickness of about 30 Å and the outer layer has a thickness of about 40Å. In yet other cases, the inner layer has a thickness of about 40 Å andthe outer layer has a thickness of about 30 Å. In further embodiments,both the inner layer and the outer layer each have a thickness of about35 Å.

In other embodiments, the base film 15 comprises or consists essentiallyof alumina and has a thickness of less than about 120 Å, perhaps lessthan about 50 Å, such as about 30 Å. Such a base film can be deposited,for example, by sputtering one or more aluminum targets in an oxidizingatmosphere. Alumina is believed to be a good sodium ion diffusionbarrier. And it may help improve performance of the coated substrate incertain testing (100% relative humidity testing).

With reference to FIGS. 4 and 5, the low-maintenance coating 80 canoptionally include one or more additional films 20 between the base film15 and the film comprising titania 50. While a single intermediate film20 is shown in FIGS. 4 and 5, multiple intermediate films can beprovided, if so desired. When provided, such film(s) 20 can comprise anysuitable material. With reference to FIG. 5, the low-maintenance coating80 can optionally include a film 13 between the substrate 10 and thebase film 15. In certain cases, the film 13 is provided in directcontact with the substrate 10 and base film 15. This, however, is notrequired. When provided, film 13 optionally be a semi-conductor film. Incertain embodiments, film 13 comprises a transparent conductive oxide(TCO) film. Suitable TCO films include fluorine-doped tin oxide andindium tin oxide. In some embodiments, film 13 is provided at athickness of 10,000 Å or less, such as about 3,000 Å. By providing atransparent conductive film 13 under the low-maintenance coating 80, theoverall U value of a glazing incorporating the coated substrate can belowered.

Table 1 below, for example, shows an embodiment where thelow-maintenance coating 80 has a thicknesses of about 135 Å. It is to beappreciated, however, that the coating 80 can have much greaterthicknesses, depending on the requirements of the intended application.Smaller thicknesses are also anticipated.

Following are a few exemplary coating embodiments of the invention.

TABLE 1 (Coating #1) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania   25 ÅBase Film 15 Silica   70 Å Substrate Glass —

TABLE 2 (Coating #2) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania   25 ÅBase Film 15 Alumina   70 Å Substrate Glass —

TABLE 3 (Coating #3) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania   25 ÅIntermediate Silica   40 Å Film 20 Base Film 15 Alumina   30 Å SubstrateGlass —

TABLE 4 (Coating #4) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania   25 ÅIntermediate Alumina   40 Å Film 20 Base Film 15 Silica   30 Å SubstrateGlass —

TABLE 5 (Coating #5) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania oxide   25Å Intermediate Silica   40 Å Film 20 Base Film 15 Alumina   30 Å Semi-Transparent Conductive Oxide 3,000 Å Conductor Film 13 Substrate Glass —

TABLE 5A (Coating #5A) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania oxide   25Å Intermediate Silica   70 Å Film 20 Semi- Transparent Conductive Oxide3,000 Å Conductor Film 13 Barrier Layer Silica   500 Å Substrate Glass —

TABLE 5B (Coating #5B) Material (comprising, consisting Componentessentially of, or consisting of) Thickness Film 50 Outer portion 50b:titania and 40-45 Å tungsten oxide Inner portion 50a: titania oxide   25Å Intermediate Alumina   70 Å Film 20 Semi- Transparent Conductive Oxide3,000 Å Conductor Film 13 Barrier Layer Silica   500 Å Substrate Glass —

In each of the exemplary coatings shown in the tables above, any silicafilm can optionally be doped with alumina.

Thus, certain embodiments provide a substrate with a major surface onwhich the following films are coated in sequence, moving outwardly fromthe major surface: (1) a functional film comprising a material selectedfrom the group consisting of indium tin oxide, fluorine-containing tinoxide, and zinc aluminum oxide and (2) a thickness of film comprisingtitania, wherein only part of that thickness includes tungsten oxide.The thickness of film comprising titania includes an inner portion andan outer portion, and the inner portion is closer to the substrate thanis the outer portion. The outer portion is the part that includestungsten oxide. In some of the present embodiments, a thickness ratiodefined as the thickness of film comprising titania divided by thethickness of the functional film is between about 0.004 and about 0.08,and perhaps more preferably between about 0.004 and about 0.025. In oneexample, film 50 has a thickness of about 70 Å and the functional film(e.g., a transparent conductive oxide layer thereof) has a thickness ofabout 3,000 Å, such that the noted thickness ratio is about 0.023. Inanother example, film 50 has a thickness of about 70 Å and thefunctional film (e.g., a transparent conductive oxide layer thereof) hasa thickness of about 2,000 Å, such that the noted thickness ratio isabout 0.035. In still another example, film 50 has a thickness of about70 Å and the functional film (e.g., a transparent conductive oxide layerthereof) has a thickness of about 5,000 Å, such that the noted thicknessratio is about 0.014.

In some cases, the low-maintenance coating 80 is provided on one majorsurface of the substrate and another functional coating 70 is providedon an opposite major surface of the same substrate. FIG. 6 illustratesone such embodiment. Here, the substrate 10 has a first surface 12bearing the low-maintenance coating 80 and a second surface 14 bearinganother functional coating 70. Functional coating 70 can be a singlelayer or a stack of layers. Various functional coatings can be used. Insome cases, the functional coating 70 is a low-emissivity coating. Insome embodiments, the coating 70 includes three or moreinfrared-reflective layers (e.g., silver-containing layers).Low-emissivity coatings with three or more infrared-reflective layersare described in U.S. patent application Ser. Nos. 11/546,152,11/545,323, 11/545,231, 11/545,212, 11/545,211, 11/398,345, and11/360,266, the salient teachings of each of which are incorporatedherein by reference. In other cases, the functional coating can be a“single silver” or “double silver” low-emissivity coating, which arewell-known to skilled artisans. When provided, functional coating 70 canalternatively comprise a transparent conductive oxide (or “TCO”) layer.Useful examples include fluorine-doped tin oxide, indium tin oxide, andzinc aluminum oxide to name just a few.

With reference to FIGS. 7 and 8, the substrate 10 can optionally be atransparent pane that is part of an insulating glazing unit 110.Typically, an insulating glazing unit 110 has an exterior pane 10 and aninterior pane 10′ separated by a between-pane space 800. A spacer 900(which can optionally be part of a sash) is commonly provided toseparate the panes 10 and 10′. The spacer 900 can be secured to theinterior surfaces of each pane using an adhesive or seal 700. In somecases, an end sealant 600 is also provided. In the illustratedembodiment, the exterior pane 10 has an exterior surface 12 (also knownas the #1 surface) and an interior surface 14 (also known as the #2surface). The interior pane 10′ has an interior surface 16 (also knownas the #3 surface) and an exterior surface 18 (also known as the #4surface). The unit can optionally be mounted in a frame (e.g., a windowframe) such that the exterior surface 12 of the exterior pane 10 isexposed to an outdoor environment 77 while the exterior surface 18 ofthe interior pane 10′ is exposed to a room-side interior environment.Interior surfaces 14 and 16 are both exposed to the atmosphere in thebetween-pane space 800 of the insulating glazing unit.

In the embodiment of FIG. 7, the exterior surface 12 of pane 10 has thelow-maintenance coating 80. In the embodiment of FIG. 8, the exteriorsurface 18 of pane 10′ has the low-maintenance coating 80. In otherembodiments, both of the exterior major surfaces of an IG unit can havelow-maintenance coatings. The coating(s) 80 can be in accordance withany embodiment described in this disclosure. In certain cases, thecoating 80 is any of the coatings described in Tables 1-5B. In otherwords, the coatings 1-5B in Tables 1-5B can be provided on exteriorsurface 12, exterior surface 18, or both. The interior surface 14 ofpane 10 can optionally have a functional coating 70, such as alow-emissivity coating, a transparent conductive oxide coating, etc. TheIG unit can have two, three or more panes.

FIG. 9 exemplifies embodiments where the substrate 10 is a window panemounted on a window frame 95 (e.g., in an exterior wall 98 of a building99). In certain applications, the first surface of the window carriesthe low-maintenance coating 80. In some embodiments of this nature,coated surface 12 is exposed to an outdoor environment 77 (e.g., so asto be in periodic contact with rain).

The invention also provides several methods for producinglow-maintenance products. Some of these methods include depositing thelow-maintenance coating 80. In such methods, each film of the coating 80can be deposited by a variety of well known coating techniques. Suitablecoating techniques include, but are not limited to, chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition, pyrolyticdeposition, sol-gel deposition and sputtering. In preferred embodiments,the films are deposited by sputtering. Sputtering is well known in thepresent art.

FIGS. 10-12 each schematically depict a coat zone 200 that can be usedto deposit one or more films of the low-maintenance coating 80. FIGS.10-12 depict six targets above and/or below the path of substrate travelin each coat zone. One or more of the adjacent target pairs, however,can be replaced with a single target, if so desired. In practice, eachadjacent pair of targets may be in its own chamber (or “bay”), and thechambers may be grouped into separate coat zones. Since many differenttypes of coaters can be used, these details are by no means limiting.

Magnetron sputtering chambers and related equipment are commerciallyavailable from a variety of sources (e.g., Applied Materials). Usefulmagnetron sputtering techniques and equipment are described in U.S. Pat.No. 4,166,018, issued to Chapin, the salient teachings of which areincorporated herein by reference. In FIGS. 10-12, each coat zone 200 isshown as being a single chamber that includes a base (or “floor”) 220, aplurality of side walls 222, and a ceiling (or “top lid” or “cover”)230, together bounding a sputtering cavity 202. As noted above, though,the coat zone may actually comprise a series of chambers. The chamberscan also be connected by a series of tunnels or inter-stage sections.The substrate 10 is conveyed along the path of substrate travel 45during film deposition, optionally over a plurality of spaced-aparttransport rollers 210.

In FIG. 10, upper targets 270 a-270 f are mounted above the path ofsubstrate travel 45. Thus, the coat zone of FIG. 10 operates as adownward sputtering chamber. In FIG. 11, lower targets 280 a-280 f aremounted beneath the path of substrate travel 45. Thus, the coat zone ofFIG. 11 operates as an upward sputtering chamber. In FIG. 12, both uppertargets 270 a-270 f and lower targets 280 a-280 f are provided. Thus,one or more films of the low-maintenance coating 80 can be sputterdeposited onto one side of the substrate, while one or more films ofanother functional coating 70 are simultaneously sputtered onto theother side of the substrate. Thus, the coat zone of FIG. 12 can operateas a dual-direction sputtering chamber. Dual-direction sputteringchambers are described in U.S. Pat. No. 6,964,731, the teachings ofwhich concerning dual-direction sputtering chambers are incorporatedherein by reference. FIGS. 10 and 11 each show six total targets, andFIG. 12 shows 12 total targets, but this is by no means required.Rather, any suitable number of targets can be provided, for example twotargets or four targets. Moreover, FIGS. 10-12 show cylindrical targets,but planar targets can also be used (in combination with, or in placeof, cylindrical targets).

In certain embodiments, the substrate 10 is subjected to one or moreheat treatments. The substrate, for example, can optionally be heattreated before and/or after the low-maintenance coating has beendeposited. The substrate can also be heat treated during deposition ofthe low-maintenance coating. For example, the substrate can optionallybe heated in one or more chambers in which at least part of the filmcomprising titania is deposited. In certain embodiments, the substrateis heat treated after deposition of the inner portion 50 a but beforethe deposition of the outer portion 50 b. In other embodiments, thesubstrate is heat treated before deposition of the inner portion 50 aand again before the deposition of the outer portion 50 b. In stillother embodiments, the substrate is heat treated after deposition ofboth the inner portion 50 a and outer portion 50 b. In furtherembodiments, the substrate is heat treated during deposition of theinner portion 50 a and/or the outer portion 50 b. In some embodiments,the low-maintenance coating 80 can include a base film 15 and thesubstrate is heat treated before, after, or during deposition of thebase film 15. It is to be appreciated, however, that the low-maintenancecoating is not required to undergo any heating before, during, or afterdeposition.

In some embodiments, heat treatment occurs in a heating chamber that ispart of a coater. Reference is made to FIGS. 13 and 14, which illustratetwo exemplary heating chambers 300. Here, the heating chamber 300includes a base (or “floor”) 320, a plurality of side walls 322, and aceiling (or “top lid” or “cover”) 330, together bounding a heatingcavity 202. When provided, the heating device 370, 380 is adjacent tothe path of substrate travel. In FIG. 13, the heating device 370 ismounted above the path of substrate travel. The heating chamber of FIG.13 may be particularly useful for heating a substrate on which alow-maintenance coating is deposited by downward sputtering, such as ina downward sputtering chamber (as illustrated by FIG. 10) or adual-direction sputtering chamber (as illustrated by FIG. 12). In FIG.14, the heating device 380 is mounted beneath the path of substratetravel. The heating chamber of FIG. 14 may be particularly useful forheating a substrate on which a low-maintenance coating is deposited byupward sputtering, such as in an upward sputtering chamber (asillustrated by FIG. 11) or a dual-direction sputtering chamber (asillustrated by FIG. 12). The heating device 370, 380 can also be used inconjunction with deposition methods other than sputtering.

The heating device 370, 380 can include any device known in the art forheating glass substrates or the like. The device 370, 380, for example,can be a resistance heater. In certain embodiments, the heating deviceincludes ceramic heaters, such as radiant quartz heaters. One suitableheater is a High Intensity Quartz Faced Radiant Heater sold commerciallyby Chromalox, Inc., a corporation having its headquarters in Pittsburgh,Pa, USA. In other embodiments, flash lamps are used for heating. Ceramicinfrared heaters are available from a variety of commercial suppliers,such as National Plastic Heater Sensor & Control Inc. (Scarborough,Ontario, Canada).

While FIGS. 13 and 14 illustrate heating chambers that perform the heattreating, heat treatments can instead (or additionally) be performed atother locations inside a coater. For example, the heat treatments can beperformed inside a deposition chamber, such as inside a sputteringchamber. In some cases, a heating device is provided inside thedeposition chamber to accomplish the heat treatment. For example, theheating device can be mounted below the path of substrate travel 45 in adownward deposition chamber (such as a downward sputtering chamber). Asanother alternative, the heating device can be mounted above the path 45in an upward deposition chamber (such as an upward sputtering chamber).The heating device can be mounted at a position inside a depositionchamber upstream from where deposition takes place, downstream fromwhere deposition takes place, or at a location where deposition takesplace.

In other cases, heating occurs inside a deposition chamber by adjustingthe deposition parameters to increase the temperature of the substrate.Methods of adjusting the deposition parameters are known to skilledartisans and need not be discussed in detail. In some cases, thedeposition chamber is a sputtering chamber and helium or hydrogen can beadded to the sputtering atmosphere. In other cases, AC sputtering can beused, rather than DC sputtering, so as to increase the temperature ofthe substrate. Thus, the substrate can optionally be heated in thedeposition chamber(s) that deposit the film 50 comprising titania, andthe heating may be caused at least in part by the sputtering processitself.

In other embodiments, heat treatment can take place at an inter-stagesection 400 of a coater (i.e., in a non-deposition section betweenneighboring deposition chambers). In some cases, the inter-stage section400 comprises a tunnel. FIG. 15 illustrates an inter-stage section 400connecting a heating chamber 300 and a sputtering chamber 200. Skilledartisans will understand that the inter-stage section 400 can instead beconnecting two sputtering chambers or other sections of a coater.Preferably, transport rollers extend from one chamber, through theinter-stage section 400, and into the next chamber. The substrate thustravels from one chamber to the next by passing through section 400.Typically, as substrates are transported from one chamber to the next,heat from the substrate is lost. Thus, in certain embodiments, theinter-stage section 400 is adapted to allow the substrate to retainheat, so that as the substrate is transported through it, heat loss isminimized. In some cases, a heating device is provided in theinter-stage section 400. In other cases, the inter-stage section 400 isheated by an external heating source, for example a radiant heater.

In certain embodiments, there is provided a production method wherein alow-emissivity coating is sputter deposited onto one major surface ofthe substrate, and thereafter at least part of the low-maintenancecoating is deposited onto the other major surface of the substrate. Insome embodiments of this nature, the sputter deposition of thelow-emissivity coating heats the substrate, and the deposition of thelow-maintenance coating is initiated while the substrate is still hot(i.e., before it has cooled to room temperature) from the sputtering ofthe low-emissivity coating. This may improve the photoactivity,hydrophilicity, morphology, or other characteristic of thelow-maintenance coating.

In some embodiments, the inter-stage section 400 is fabricated ofmaterial that holds heat. FIG. 15 illustrates one embodiment of aninter-stage section 400 that is constructed so that it maintains heat.Referring to FIG. 16, section 400 can optionally have a base (or“floor”) 420, side walls 422, and a ceiling 430, together bounding aninterior space 402 that houses transport rollers 210 that transport asubstrate 10. The base 420, side walls 422, and ceiling 430 form arectangular tunnel, but other shapes, for example square and circulartunnels, are within the scope of the invention. Preferably, the base420, side walls 422, and ceiling 430 are formed as a single piece, forexample like a matchbox slip. In FIG. 16, the section 400 has a layeredconfiguration, including layers of a conductive material 450 surroundedby layers of a ceramic material 470. In the illustrated embodiment,three layers of conductive material 450 and three layers of ceramicmaterial 470 are shown, but any suitable number of layers can beprovided. The layer of conductive material 450 can include anyconductive metal, such as aluminum or copper. The layer of ceramicmaterial 470 can include any dielectric that prevents heat from escapingoutwards. Such ceramic may include silicon nitride, magnesium oxide,calcium oxide, zirconia, alumina, chromite, silicon carbide, carbon, andmullite. A heating source 500 can be provided, for example a radiantheater that applies heat to one or more of the conductive layers 450.Such a layered configuration may help to maintain the heat inside theexterior 402. In some embodiments, the interior space is maintained at atemperature of at least 160° F.

In certain cases, heating can take place at an “intermediate position”on the path of substrate travel. This so-called intermediate position isbetween an upstream location on the path 45 (where the inner portion 50a is deposited) and a downstream location on the path 45 (where theouter portion 50 b is deposited). The intermediate position can beinside a sputtering chamber adapted for depositing at least part of theinner portion 50 a, the position being located a point after suchsputtering deposition has taken place. The intermediate position canalso be inside a sputtering chamber adapted for depositing at least partof the outer portion 50 b, the position being located a point beforesuch sputtering deposition takes place. The intermediate position canalternatively be inside a heating chamber located between two sputteringchambers that respectively deposit the inner portion 50 a and the outerportion 50 b. The intermediate position can be inside an inter-stagesection that connects sputtering chambers that respectively deposit theinner portion 50 a and the outer portion 50 b. Such heating can beaccomplished, for example, by providing a heating device at the desiredintermediate position(s).

FIGS. 17 and 18 schematically illustrate two exemplary coaters that canbe used to produce the low-maintenance coating, in accordance withcertain embodiments. FIG. 17 illustrates a coater having downwardcoating chambers 200 a, 200 b, 200 c, and 200 d (shown here with uppersputtering targets 270 a-270 x) and a downward heating chamber 300 (withupper heating device 370). FIG. 18 illustrates a coater having upwardcoating chambers 200 a, 200 b, 200 c, and 200 d (shown here with lowersputtering targets 280 a-280 x) and an upward heating chamber (withlower heating device 380). A substrate is conveyed along the path ofsubstrate travel 45 through the coater in the following order: coatingchamber 200 a, inter-stage section 400 a, coating chamber 200 b,inter-stage section 400 b, coating chamber 200 c, inter-stage section400 c, heating chamber 300, inter-stage section 400 d, and coatingchamber 200 d. In certain embodiments, the coating chambers 200 a and200 b are used to deposit a base film 15 and/or any intermediate films20, and the coating chambers 200 c and 200 d are used to deposit thefilm comprising titania 50 (chamber 200 c is used to deposit the innerportion 50 a, and chamber 200 d is used to deposit the outer portion 50b). Here, the heating chamber 300 is used to heat the substrate afterthe inner portion 50 a has been deposited, but before the outer portion50 b is deposited. However, the heating chamber 300 can alternatively(or additionally) be provided at other locations in the coater, forexample before chamber 200 a, before chamber 200 b (and after chamber200 a), before chamber 200 c (and after chamber 200 b), and/or afterchamber 200 d. If desired, additional coating chambers can be providedin embodiments where additional films are provided.

In certain embodiments, a base film 15 is deposited in coating chambers200 a and 200 b. In these embodiments, the coating chambers 200 a and200 b can optionally be provided with targets carrying the samesputterable material (270 a-270 f, 280 a-280 f). In other embodiments,the base film 15 is deposited in coating chamber 200 a and anintermediate film 20 is deposited in coating chamber 200 b. In theseembodiments, the coating chamber 200 a is provided with the samesputterable material (270 a-270 f, 280 a-280 f) for depositing a basefilm 15 and the coating chamber 200 b is provided with anothersputterable material (270 g-270 l, 280 g-280 l) for depositing anintermediate film 20.

The sputterable material can be a metal, a semi-metal, a compound ofdifferent metals, a compound of at least one metal and at least onesemi-metal, etc., In such cases, an oxidizing atmosphere (optionallyincluding some argon and/or nitrogen) may be used for sputtering. Thetargets can alternatively be ceramic (e.g., metal oxide), and an inert(or slightly oxidizing and/or slightly nitriding) atmosphere may beused. In embodiments where the base film 15 comprises silica, targetscomprising silicon may be used. The targets comprising silicon, forexample, may be silicon-aluminum targets. Likewise, in embodiments wherethe base film 15 comprises alumina, targets comprising aluminum can beused. In cases where the base film 15 is provided, it can alternativelycomprise tin oxide, zirconium oxide, another dielectric, or asemiconductor.

In embodiments where the base film 15 is a mixed oxide film, aco-sputtering method can optionally be used. For example, some of thetargets in a particular chamber can optionally comprise one sputterablematerial while other targets in the same chamber comprise anothersputterable material. For example, if coating chamber 200 a is used todeposit a base film 15, targets 270 a, 270 c, and 270 e (or targets 280a, 280 c, 280 e) comprise material A and targets 270 b, 270 d, and 270 f(or targets 280 b, 280 d, and 280 f) comprise material B. Likewise, ifboth coating chambers 200 a and 200 b are used to deposit a base film15, targets 270 a, 270 c, 270 e, 270 g, 270 i, and 270 k (or targets 280a, 280 c, 280 e, 280 g, 280 i, and 280 k) comprise material A andtargets 270 b, 270 d, 270 f, 270 h, 270 j, and 270 l (or targets 280 b,280 d, 280 f, 280 h, 280 j, and 280 l) comprise material B.

The targets, for example, can be metal targets and an oxidizingatmosphere (optionally including argon and/or nitrogen) can be used. Thetargets can alternatively be ceramic, and an inert (or slightlyoxidizing and/or slightly nitriding) atmosphere can be used. Forexample, in embodiments where the base film 15 is a mixed oxide filmcomprising silica and titania, material A can comprise silicon andmaterial B can comprise titanium. Any intermediate film(s) 20 having amixed oxide film can be deposited in the same manner as a mixed oxidebase film.

With continued reference to FIGS. 17 and 18, once the base film 15and/or any intermediate films 20 are deposited, the substrate travelsthrough chamber 200 c, where the inner portion 50 a of the filmcomprising titania 50 is deposited. In embodiments where the innerportion 50 a is a substantially homogenous film, the targets 270 m-270r, 280 m-280 r can all carry the same sputterable material. Thesetargets, for example, can be metal, and an oxidizing atmosphere can beused. The targets can alternatively be ceramic, and an inert (orslightly oxidizing) atmosphere can be used. In embodiments where theinner portion 50 a consists essentially of titania, targets comprisingtitanium can be used. The targets comprising titanium can be titaniummetal and an oxidizing atmosphere can be used, or titanium oxide targetscan be used with an inert (or slightly oxidizing) atmosphere. Whentitanium oxide targets are used, they can optionally besubstoichiometric titanium oxide targets, which are sold commercially byBekaert NV (Deinze, Belgium).

In the exemplary embodiments of FIGS. 17 and 18, once the inner portion50 a is deposited in chamber 200 c, the substrate 10 travels through aheating chamber 300, where a heater 370, 380 supplies heat to thesubstrate. Again, it is to be appreciated that the heater can beomitted, if so desired. The substrate then travels through coater 200 d,where the outer portion 50 b of the film 50 is deposited.

If the substrate is annealed glass, it may be preferred not to heat theglass to temperatures that will adversely affect the annealed state ofthe glass. For example, maximum glass temperatures below 350° F. arepreferred, and temperatures below 250° F. are more preferred. In someembodiments, the substrate is heated to a maximum temperature of between140° F. and 350° F., such as between about 170° F. and about 210° F. Itis to be appreciated that the substrate is not required to be heatedprior to or during deposition. Instead, the coated substrate may be heattreated after deposition. Or, the coated substrate may be producedwithout heat treatment.

In embodiments where the outer portion 50 b comprises both titania andtungsten oxide, the targets (270 r-270 w, 280 r-280 w) can each carry asputterable material comprising both titanium and tungsten. In one groupof embodiments, the sputterable material includes titanium and tungsten,wherein the titanium is in the form of metal titanium, titaniummonoxide, titanium dioxide and/or titanium trioxide, and the tungsten isin the form of metal tungsten, tungsten oxide, tungsten dioxide, and/ortungsten trioxide. In some cases, the sputterable material comprisesboth titanium and tungsten in a variety of the above forms.

In certain embodiments, the sputterable material consists essentially oftitanium metal and tungsten metal. An alloy target comprising bothtitanium and tungsten could be used. Or, one could use a metal titaniumtarget provided with strips (or the like) of metal tungsten. Anotherpossibility is a metal alloy target with tungsten metal strips attached.When metal targets are sputtered, an oxidizing atmosphere (optionallywith a slight amount of nitrogen) can be used. In other cases, thesputterable material comprises both titanium oxide and tungsten oxide.In these cases, an inert atmosphere or slightly oxidizing atmosphere(optionally with a slight amount of nitrogen) can be used. In certainembodiments, the sputterable material comprises titanium monoxide,titanium dioxide, and tungsten oxide. In these cases, a slightlyoxidizing atmosphere (optionally with a slight amount of nitrogen) canbe used. Or, the targets could be sputtered in an inert atmosphere,e.g., if the resulting film is not required to be fully oxidized. Incertain cases, the sputterable material is characterized by a metal-onlyatomic ratio of between about 0.01 and 0.34, this ratio being the numberof tungsten atoms in the sputterable material divided by the number oftitanium atoms in the sputterable material.

A target with sputterable material comprising both titanium and tungstencan be prepared using a number of different methods. In someembodiments, a target is prepared by plasma spraying titanium oxidetogether with tungsten metal onto a target base in an atmosphere that isoxygen deficient and does not contain oxygen-containing compounds.During the plasma spraying process, the action of the plasma on thetitanium oxide causes the titanium oxide to lose some oxygen atoms fromtheir lattices. These oxygen atoms are believed to combine with themetal tungsten to form tungsten oxide, as tungsten has a highelectrochemical potential. The titanium oxide sprayed onto the backingtube may thus comprise titanium monoxide, titanium dioxide, and tungstenoxide. The sputterable target may, as just one example, be a cylindricalrotary target having a backing tube with a length of at least 24 inches.In such cases, the sputterable material is carried on an exterior wallof the backing tube. Such a cylindrical target is also adapted to rotateabout a central axis to which the exterior wall of the backing tube issubstantially parallel. Alternatively, hot isostatic pressing may beused to form a target. Other target forming methods may also be used.

When the outer portion 50 b is deposited by sputtering one or moretargets comprising substoichiometric TiOx, the sputtering is preferablycarried out using argon, a mixture of argon and oxygen, a mixture ofnitrogen and argon, a mixture of nitrogen and oxygen, or a mixture ofoxygen, nitrogen, and argon. If the plasma gas does not contain oxygen,e.g., if pure argon is used, then the coating will not be fully oxidizedwhen deposited. In contrast, if the plasma gas contains oxygen, then thereduced form(s) of titanium oxide may be converted during the sputteringprocess into the transparent form, which is stoichiometric orsubstantially stoichiometric. A film comprising titania and tungstenoxide can be produced in this way. The degree of transparency of thefilm will depend upon the amount of oxygen contained in the plasma gas.An exemplary gas mixture to form transparent film is 70-90% by volumeargon and 30-10% by volume of oxygen. In some cases, the gas mixture caninclude 1-3% by volume oxygen, with the remainder being argon.

In embodiments where the outer portion 50 b is a film comprising bothtitania and tungsten oxide, a co-sputtering method can optionally beused. For example, one target can comprise titanium metal while anadjacent target comprises tungsten metal. For example, targets 270 s,270 u, and 270 w (or targets 280 s, 280 u, and 280 w) can each comprisematerial A, while targets 270 t, 270 v, and 270 x (or targets 280 t, 280v, and 280 x) each comprise material B, and one of material A or B cancomprise titanium while the other of materials A and B comprisestungsten. As still another option, the targets used to deposit the outerportion 50 b can carry a sputterable metallic material that is acompound (e.g., an alloy) comprising both titanium metal and tungstenmetal.

After the substrate has been coated with the low-maintenance coating 80,the coated substrate can optionally be subjected to a post-depositionheat treatment. In certain embodiments, the coated substrate ispositioned in a heating chamber for at least 60 seconds, during whichtime the heating chamber is maintained at a temperature of at least 650°C. Preferably, the heat treatment brings the coated substrate to atemperature of at least about 640° C. After heat treatment, thesubstrate is cooled back down to room temperature, at which point thecoated substrate preferably exhibits a haze of less than 0.4 (morepreferably less than 0.2, or even less than 0.15) after heat treatment.

Some exemplary film stacks and deposition methods will now be described,in accordance with certain embodiments.

EXAMPLE #1

The coating shown in Table 1 (“Coating #1) was deposited according tothe following method. A soda-lime glass substrate was transportedthrough the coating line shown in FIG. 19. Chambers 200 a and 200 b eachhave six lower silicon targets (each including a small amount ofaluminum). An oxidizing atmosphere was provided in each chamber and thesilicon targets were sputtered upwardly to deposit a base filmcomprising silica on the surface 12 of the substrate. The base film hada thickness of about 70 Å. Next, the substrate was transported throughanother chamber 200 c, which had six lower titanium metal targets. Anoxidizing atmosphere was provided, and the titanium targets weresputtered upwardly to deposit the inner portion 50 a of a filmcomprising titania on the base film. The inner portion consistedessentially of titanium oxide, and had a thickness of about 25 Å. Next,the substrate was transported through a heating chamber 300 having alower heater 380 for heating the substrate. The heater 380 was a HighIntensity Quartz Faced Radiant Heater, obtained from Chromalox, Inc.(When a heater is used, however, it may be desirable to use a heaterthat operates by other than radiative heating.) In this example, thechamber 300 was actually an inter-stage chamber located between coatzones 200 c and 200 d. Next, the substrate was transported through achamber 200 d having six lower targets each carrying a sputterablematerial comprising both titania and tungsten oxide. An atmosphere ofargon and oxygen was provided, and the targets were sputtered upwardlyto deposit the outer portion 50 b of the film 50 on the inner portion 50a. The outer portion 50 b consisted essentially of titania and tungstenoxide, and it had a thickness of about 40-45 Å. The substrate wasconveyed through these chambers and the heating chamber at a speed ofabout 250 inches per minute.

Once the coating was deposited, the glass was tempered in a mannerbelieved to yield acceptable tempering in a commercial productionsetting. In particular, the coated glass was washed using standardwashing equipment and placed in a furnace maintained at about 680-705°C. (preferably controlled to 690-700° C.). The coated glass was held inthe furnace for 100-120 seconds with constant movement to better ensuretemperature uniformity, so as to raise the glass temperature to about640° C. The glass was then removed from the furnace and positioned in astream of air for about 50 seconds until the glass was cool enough foran operator to handle. The haze of the tempered glass was measured usinga hazometer sold by BYK Gardner under the trade name Haze-Gard Plus anda reading of 0.12 was obtained.

EXAMPLE #2

The coating shown in Table 3 (“Coating 3”), can be deposited accordingto the following method. A soda-lime glass substrate can be transportedthrough the coating line shown in FIG. 20. Chamber 200 a has six loweraluminum targets and an oxidizing atmosphere can be provided. Thealuminum targets can be sputtered upwardly to deposit a base filmcomprising alumina on the surface 12. The base film can have a thicknessof about 30 Å. Next, the substrate can be transported through anotherchamber 200 b, which can include six lower silicon targets. An oxidizingatmosphere can be provided and the silicon targets can be sputteredupwardly to deposit an intermediate film comprising silica directly ontothe base film. Next, the substrate can be transported through anotherchamber 200 c, which can include six lower titanium metal targets. Anoxidizing atmosphere can be provided, and the titanium targets can besputtered upwardly to deposit an inner portion 50 a of a film comprisingtitania on the intermediate film. The inner portion can have a thicknessof about 25 Å. Next, the substrate can be transported through anoptional heating chamber 300 having a lower heater 380 for heating thesubstrate. Next, the substrate can be transported through a chamber 200d having six lower targets each carrying a sputterable materialcomprising both titania and tungsten oxide. An atmosphere of argon andoxygen can be provided, and the targets can be sputtered upwardly todeposit the outer portion 50 b. The outer portion 50 b can have athickness of about 40-45 Å. The substrate can be conveyed through thesechambers at a speed of about 250 inches per minute. Once the coating isdeposited, the glass can optionally be tempered in a manner believed toyield acceptable tempering in a commercial production setting.

COMPARATIVE EXAMPLE

A coating having an outer film of titanium dioxide was prepared, and isillustrated in Table 6 (“Comparative Coating #6”).

TABLE 6 (Comparative Coating #6) Component Material Thickness Outer FilmTitanium Oxide 25-40 Å Base Film Silica   75 Å Substrate Glass —

A rate of acetone photodecomposition was determined for Coating #1 andfor Comparative Coating #6. The results are illustrated in FIG. 21. Therates were determined using a standard Fourier-transform infraredspectrometer (FTIR), which monitored a loss of acetone due tophotocatalytic activity. As shown, Coating #1 showed a rate of acetonephotodecomposition of about 2, whereas the Comparative Coating #6 showeda rate of about 1.25.

While certain preferred embodiments of the invention have beendescribed, it should be understood that various changes, adaptations andmodifications can be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A sputtering technique for depositing a low-maintenance coating overa major surface of a substrate, wherein the sputtering techniqueincludes depositing a thickness of film comprising titania, wherein atleast part of that thickness includes tungsten oxide and is deposited bysputtering one or more targets having a sputterable material comprisingboth titania and tungsten oxide, wherein the sputterable materialincludes: i) tungsten in oxide form, ii) TiO, and iii) TiO₂.
 2. Thesputtering technique of claim 1 wherein substantially all the tungstenin the sputterable material is in oxide form.
 3. The sputteringtechnique of claim 1 wherein the depositing is accomplished bysputtering the targets in an atmosphere comprising oxygen.
 4. Thesputtering technique of claim 1 wherein the sputterable material ischaracterized by a metal-only atomic ratio of between about 0.01 andabout 0.34, this ratio being the number of tungsten atoms in thesputterable material divided by the number of titanium atoms in thesputterable material.
 5. The sputtering technique of claim 1 wherein thethickness of film comprising titania includes an inner portion and anouter portion, the inner portion being closer to the substrate than isthe outer portion, wherein only the outer portion includes tungstenoxide, the outer portion being deposited as a substantially homogenousfilm comprising titanium oxide and tungsten oxide.
 6. The sputteringtechnique of claim 5 wherein the inner portion is deposited as filmconsisting essentially of titania.
 7. The sputtering technique of claim1 wherein the thickness of the film comprising titania is less than 250Å.
 8. A sputtering target having a sputterable material comprising bothtitania and tungsten oxide, wherein the sputterable material includes:i) tungsten in oxide form, ii) TiO, and iii) TiO₂.
 9. The sputteringtarget of claim 8 wherein substantially all the tungsten in thesputterable material is in oxide form.
 10. The sputtering target ofclaim 8 wherein the sputterable material is characterized by ametal-only atomic ratio between about 0.01 and about 0.34, this ratiobeing the number of tungsten atoms in the sputterable material dividedby the number of titanium atoms in the sputterable material.
 11. Thesputtering target of claim 8 wherein the sputterable material consistsessentially of: i) tungsten in oxide form, ii) TiO, and iii) TiO₂. 12.The sputtering target of claim 8 wherein the target is a cylindricalrotary target, the sputterable material being carried on an exteriorwall of an elongated backing tube, the elongated backing tube having alength of at least 24 inches, the target being adapted to rotate about acentral axis to which the exterior wall of the backing tube issubstantially parallel.
 13. A substrate having a major surface on whichthere is a low-maintenance coating, the low-maintenance coatingincluding a thickness of film comprising titania, said thickness beingless than 250 Å, wherein only part of that thickness includes tungstenoxide, said thickness including an inner portion and an outer portion,the inner portion being closer to the substrate than is the outerportion, the outer portion being the part that includes tungsten oxide.14. The substrate of claim 13 wherein the thickness of the outer portionis no more than about 90 Å.
 15. The substrate of claim 13 wherein saidthickness of film comprising titania is less than about 150 Å.
 16. Thesubstrate of claim 13 wherein the outer portion defines an exposed,outermost face of the low-maintenance coating, the outer portion being asubstantially homogenous film comprising both titanium dioxide andtungsten oxide.
 17. The substrate of claim 16 wherein the inner portionis a substantially homogenous film consisting essentially of titania.18. The substrate of claim 13 wherein the outer portion has a tungstenload characterized by a metal-only atomic ratio of between about 0.01and about 0.34, this ratio being the number of tungsten atoms in theouter portion divided by the number of titanium atoms in the outerportion.
 19. The substrate of claim 13 wherein the low-maintenancecoating includes a base film between the major surface of the substrateand said thickness of film comprising titania.
 20. The substrate ofclaim 19 wherein the base film and said thickness of film comprisingtitania have a combined thickness of less than about 150 Å.
 21. Thesubstrate of claim 19 wherein the base film comprises silica.
 22. Thesubstrate of claim 19 wherein the base film comprises alumina.
 23. Thesubstrate of claim 19 wherein the base film has a thickness of less thanabout 100 Å.
 24. The substrate of claim 13 wherein a base film isprovided between said thickness of film comprising titania and the majorsurface of the substrate, and an intermediate film is provided betweenthe base film and said thickness of film comprising titania.
 25. Thesubstrate of claim 24 wherein the base film and the intermediate filmeach have a thickness of less than 100 Å.
 26. The substrate of claim 25wherein base film comprises alumina and the intermediate film comprisessilica.
 27. The substrate of claim 26 wherein the base film comprisesalumina at a thickness of less than about 50 Å and the intermediate filmcomprises silica at thickness of less than about 50 Å.
 28. The substrateof claim 13 wherein a transparent conductive oxide film is providedbetween the major surface of the substrate and the low-maintenancecoating.
 29. The substrate of claim 28 wherein the substrate is atransparent pane that is part of a multiple-pane insulating glazing unithaving a between-pane space, wherein the major surface bearing thelow-maintenance coating faces away from the between-pane space of theunit.
 30. The substrate of claim 13 wherein the substrate is part of atriple-pane insulating glazing unit.
 31. The substrate of claim 13wherein the substrate is part of a multiple-pane insulating glazing unithaving two exterior major surfaces each bearing a low-maintenancecoating comprising titania.
 32. A substrate having a major surface onwhich the following films are coated in sequence, moving outwardly fromthe major surface: i) a functional film comprising a material selectedfrom the group consisting of indium tin oxide and fluorine-containingtin oxide; and ii) a thickness of film comprising titania, wherein onlypart of that thickness includes tungsten oxide, said thickness includingan inner portion and an outer portion, the inner portion being closer tothe substrate than is the outer portion, the outer portion being thepart that includes tungsten oxide, wherein a thickness ratio defined assaid thickness of film comprising titania divided by the thickness ofthe functional film is between about 0.004 and about 0.08.
 33. Thesubstrate of claim 32 wherein said thickness ratio is between about0.004 and about 0.025.
 34. The substrate of claim 32 wherein between thefunctional film and said thickness of film comprising titania there is alayer having a thickness of less than 100 Å.
 35. The substrate of claim32 wherein between the functional film and said thickness of filmcomprising titania there is a layer comprising silica, alumina, or both.36. The substrate of claim 32 wherein between the functional film andsaid thickness of film comprising titania there are two layers of filmhaving a combined thickness of less than 100 Å.
 37. A substrate having amajor surface on which there is both a transparent conductive oxide filmand a low-maintenance coating, the transparent conductive oxide filmbeing closer to the substrate than is the low-maintenance coating, thelow-maintenance coating including a thickness of film comprisingtitania, wherein only part of that thickness includes tungsten oxide,said thickness including an inner portion and an outer portion, theinner portion being closer to the substrate than is the outer portion,the outer portion being the part that includes tungsten oxide, whereinbetween the transparent conductive oxide film and said thickness of filmcomprising titania there are two layers including one comprising silicaand one comprising alumina.
 38. The substrate of claim 37 wherein saidtwo layers have a combined thickness of less than 100 angstroms.
 39. Thesubstrate of claim 37 wherein said layer comprising alumina is closer tothe substrate than is said layer comprising silica.
 40. The substrate ofclaim 37 wherein said layer comprising alumina is contiguous to saidlayer comprising silica.
 41. The substrate of claim 37 wherein thesubstrate is a transparent pane that is part of a multiple-paneinsulating glazing unit having a between-pane space, wherein the majorsurface bearing the transparent conductive oxide film and thelow-maintenance coating faces away from the between-pane space of theunit.
 42. A method of producing a low-maintenance product, the methodcomprising using a coater to deposit a low-maintenance coating on amajor surface of a substrate, the low-maintenance coating including athickness of film comprising titania, wherein only part of thatthickness includes tungsten oxide, wherein the thickness of filmcomprising titania includes an inner portion and an outer portion, theouter portion being the part that includes tungsten oxide, the innerportion being deposited before the outer portion is deposited, whereinheating is performed while the substrate is inside the coater.
 43. Themethod of claim 42 wherein said heating brings the substrate to amaximum temperature of greater than 140° F. but less than 350° F. 44.The method of claim 42 wherein the substrate is subjected to saidheating after the inner portion has been deposited but before the outerportion is deposited.
 45. The method of claim 42 wherein said heating isperformed inside a deposition chamber adapted for depositing at leastpart of the inner portion or at least part of the outer portion.
 46. Themethod of claim 42 wherein the low-maintenance coating is deposited in asputter coater.
 47. The method of claim 44 wherein said heating isperformed inside a heating chamber positioned between a first depositionchamber and a second deposition chamber, the first deposition chamberbeing adapted for depositing the inner portion, the second depositionchamber being adapted for depositing the outer portion.
 48. The methodof claim 44 wherein the method includes conveying the substrate throughone or more inter-stage sections that are part of said coater, saidinter-stage sections being adapted for maintaining the substrate at atemperature of at least about 160° F.
 49. The method of claim 48 whereinat least one of said inter-stage sections is positioned between a firstdeposition chamber and a second deposition chamber, the first depositionchamber being adapted for depositing the inner portion, the seconddeposition chamber being adapted for depositing the outer portion. 50.The method of claim 44 wherein the substrate is also subjected toheating before the inner portion has been deposited.
 51. The method ofclaim 44 wherein the substrate is also subjected to heating duringdeposition of either or both of the inner portion and outer portion. 52.A method of producing a low-maintenance product, the method comprisingproviding a substrate having a major surface on which there is alow-maintenance coating, the low-maintenance coating including athickness of film comprising titania, said thickness being greater thanabout 50 Å but less than 250 Å, wherein only part of that thicknessincludes tungsten oxide, said thickness including an inner portion andan outer portion, the inner portion being closer to the substrate thanis the outer portion, the outer portion being the part that includestungsten oxide, the method further comprising heat treating said coatedsubstrate to bring said coated substrate to a temperature of at leastabout 160° F.
 53. The method of claim 52 wherein the heat treating isaccomplished by positioning said coated substrate in a heating chamberfor at least 60 seconds during which time the heating chamber ismaintained at a temperature of at least 650° C.
 54. The method of claim52 further comprising cooling said coated substrate back down to roomtemperature, at which point said coated substrate exhibits a haze ofless than about 0.4.
 55. A sputter coater, comprising: a chamberselected from the group consisting of a sputtering chamber and a heatingchamber; at least one inter-stage section extending from said chamber,the inter-stage section having an interior space surrounded byalternating layers of a conductive metal and a ceramic material; atleast one heating source adapted to apply heat to the inter-stagesection, so that the interior space is adapted for being maintained at atemperature of at least about 160° F.
 56. The sputter coater of claim 55wherein the inter-stage section connects two sputtering chambers. 57.The sputter coater of claim 55 wherein the coater is adapted fordepositing a thickness of film comprising titania, wherein only a partof that thickness includes tungsten oxide, said thickness including aninner portion and an outer portion, the inner portion being closer tothe substrate than is the outer portion, the outer portion being thepart that includes tungsten oxide.
 58. The sputter coater of claim 57wherein said inter-stage section connects a first sputtering chamberthat is adapted for depositing the inner portion and a second sputteringchamber that is adapted for depositing the outer portion.